U.S. patent number 7,150,410 [Application Number 10/724,480] was granted by the patent office on 2006-12-19 for method for providing a controlled injection rate and injection pressure in a fuel injector assembly.
This patent grant is currently assigned to Robert Bosch GmbH. Invention is credited to Robert D. Straub.
United States Patent |
7,150,410 |
Straub |
December 19, 2006 |
Method for providing a controlled injection rate and injection
pressure in a fuel injector assembly
Abstract
A method for controlling injection rate and injection pressure
of an electromagnetic fuel injector assembly having a pressure
balanced control valve including a solenoid and a valve member
subject to the pressure developed by the injector and actuated by
the solenoid to close the valve member against the biasing force of
a spring. The control valve is supported in a valve bore in an
injector body. The method includes the step of providing a first
level of current to the solenoid for moving the valve member from
an open to a closed position allowing the pressure in the injector
to rise, providing a regulated current to the solenoid at
preselected times during the injector event to unbalance the forces
acting on the valve member thereby slightly unseating the valve
member to regulate injection pressure and injection rate of the
fuel injector, and ending solenoid current delivery thereby moving
the valve member to its open position.
Inventors: |
Straub; Robert D. (Lowell,
MI) |
Assignee: |
Robert Bosch GmbH (Stuttgart,
DE)
|
Family
ID: |
37526493 |
Appl.
No.: |
10/724,480 |
Filed: |
November 28, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
09245106 |
Jan 29, 1999 |
|
|
|
|
Current U.S.
Class: |
239/5; 239/88;
239/533.7 |
Current CPC
Class: |
F02M
45/12 (20130101); F02M 63/0031 (20130101); F02M
63/0015 (20130101); F02M 59/366 (20130101); F02D
41/40 (20130101); F02D 41/20 (20130101); F02M
57/023 (20130101); Y02T 10/40 (20130101); Y02T
10/44 (20130101) |
Current International
Class: |
F02D
1/06 (20060101) |
Field of
Search: |
;239/5,88,93,95,96,533.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1 055 814 |
|
Nov 2000 |
|
EP |
|
760852 |
|
Nov 1956 |
|
GB |
|
134363 |
|
Dec 1948 |
|
SE |
|
WO 00/34644 |
|
Jun 2000 |
|
WO |
|
Primary Examiner: Kim; Christopher
Attorney, Agent or Firm: Brooks Kushman P.C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of U.S. application Ser.
No. 09/245,106, filed Jan. 29, 1999 now abandoned, entitled "Method
and Apparatus for Providing a Controlled Injection Rate and
Injection Pressure in a Fuel Injector Assembly", now abandoned.
Applicant claims the benefit of that application.
Claims
What is claimed is:
1. A method for controlling injection rate and injection pressure
of a liquid fuel injector having a nozzle assembly and an injector
plunger in an injector cylinder for developing nozzle assembly
injection pressure, a pressure balanced control valve assembly
including a valve body with a valve bore defining a valve seat, a
movable valve element in the valve bore with a valve head on the
movable valve element, the valve head and the valve seat defining a
liquid fuel flow opening, the movable valve element communicating
with a pressure regulated nozzle passage whereby the valve element
is subject to injection pressure developed by the fuel injector
plunger when it is stroked during an injection event, the valve
seat and the valve head defining in part a fluid pressure spill
passage communicating with the pressure regulated nozzle passage,
the spill passage communicating with a fluid supply passage whereby
the injector cylinder is supplied with liquid fuel when the fuel
injection plunger is retracted, a solenoid actuator for the movable
valve element, the valve seat and the valve head being normally
open with the solenoid de-energized, and a spring acting on the
valve element to oppose a solenoid actuator force; the method
comprising the steps of: providing a first level of regulated
current to the solenoid actuator to activate the movable valve
element causing the valve head to move toward the valve seat to a
first pressure regulating position defining a reduced liquid fuel
flow opening whereby the spill flow passage has a first degree of
fuel flow restriction thereby allowing regulated injection pressure
in the nozzle assembly to rise and creating an initial liquid fuel
injection pulse in an initial injection rate-controlled fuel
injection period; providing a second reduced level of regulated
current to the solenoid actuator for a preselected time following
the initial liquid fuel injection pulse during an injection event
to move the valve head away from the valve seat to a second
pressure regulating position and to define an increased liquid fuel
flow opening thereby creating a reduced initial injection pressure
during the initial injection rate-controlled period; and providing
a third level of regulated current at a value to cause the valve
head to move toward the valve seat to a third pressure regulating
position to define a decreased liquid fuel flow opening thereby
creating a high third injection pressure regulating position that
allows regulated injection pressure in the nozzle assembly to rise
further during a main injector rate-controlled fuel injection
period and to create a peak injection pressure pulse near the end
of the injection event.
2. The method set forth in claim 1 wherein the step of providing a
third level of regulated current includes the step of maintaining
the third level of regulated current during the main injection
rate-controlled fuel injection period, thereby maintaining the peak
injection pressure pulse for a precalibrated time near the end of
the injection event.
3. The method set forth in claim 2 wherein the step of providing
the third level of regulated current is followed by the step of
controlling depressurization of the nozzle assembly at the end of
the main injection rate-controlled period.
4. The method set forth in claim 3 wherein the step of providing
the third level of regulated current is preceded by a step of
increasing the regulated pressure at a controlled rate following
the initial injection rate-controlled period.
5. The method set forth in claim 3 wherein the step of controlling
depressurization of the nozzle assembly comprises the steps of
reducing the level of current to a first lower depressurization
control level following the step of providing the third level of
regulated current and reducing the level of current further to a
second lower depressurization control level thereby terminating the
injection event.
6. The method set forth in claim 4 wherein the step of controlling
depressurization of the nozzle assembly comprises the steps of
reducing the level of current to a first lower depressurization
control level following the step of providing the third level of
regulated current and reducing the level of current further to a
second lower depressurization control level thereby terminating the
injection event.
7. A method for controlling injection rate and injection pressure
of a liquid fuel injector having a nozzle assembly and an injector
plunger in an injector cylinder for developing nozzle assembly
injection pressure when it is stroked, a pressure-balanced control
valve including a solenoid actuator and a valve element subject to
pressures developed by the injector plunger, the valve element
being actuated by the solenoid to apply a force on the valve
element for metering fuel flow to the injector nozzle assembly, a
valve spring acting on the valve element and opposing a solenoid
actuator force, the valve element having a valve head surrounded by
a valve seat and defining with the valve seat a fuel flow spill
passage, the valve element controlling the injection pressure
between an initial pressure and a maximum pressure, the method
including the steps of: providing a first level of current to the
solenoid actuator for moving the valve element from a normally open
position toward a closed position to a first pressure regulating
position allowing injection pressure to rise in an initial
rate-controlled period; providing a reduced level of current to the
solenoid actuator following the initial rate-controlled period to
reduce the force on the valve element and to move the valve head
away from the valve seat, thereby regulating the pressure to reduce
the rate of injection of the fuel as the valve element assumes a
second pressure regulating position; providing an increased level
of current to the solenoid actuator following the initial
rate-controlled period for moving the valve element toward its
closed position to a third fuel pressure regulating position to
effect increased pressure regulation and a peak injection pressure
value during a peak injection rate-controlled period; providing a
further reduced level of current to the solenoid actuator following
the peak injection rate-controlled period to move the valve element
under spring force to a depressurization position; and ending
solenoid actuator current delivery thereby moving the valve away
from the valve seat to its fully open position at the end of an
injection event.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a method for controlling
injection rate and injection pressure in an electromagnetic fuel
injector. More specifically, the invention relates to a method for
controlling injection rate and injection pressure by varying
current to a solenoid-actuated control valve to improve the
operational characteristics of the fuel injector.
2. Background Art
Fuel injector assemblies are employed in internal combustion
engines for delivering a predetermined, metered mixture of fuel and
air to the combustion chamber at preselected intervals. In the case
of compression ignition engines and diesel engines, the fuel/air
mixture is delivered at relatively high pressures. Presently,
conventional injectors deliver this mixture at pressures as high as
32,000 psi. These fairly high pressures require considerable
engineering attention to ensure the structural integrity of the
injector, good sealing properties, and the effective atomization of
the fuel within the combustion chamber. However, increasing demands
for greater fuel economy, cleaner burning, fewer emissions and
NO.sub.x control have placed, and will continue to place, even
higher demands on the engine's fuel delivery system, including
increasing the fuel pressure within the injector.
Fuel injectors presently employed in the related art typically
include a high pressure fuel passage, which extends between a
solenoid-actuated control valve and the plunger cylinder in the
injector body. Fuel at relatively low pressure is supplied to the
control valve, which then meters the delivery of the fuel at very
high pressures and at predetermined intervals through the high
pressure fuel passage to the plunger cylinder. The fuel ultimately
exits the injector through a fuel nozzle.
The solenoid-actuated control valve is supported in a stepped bore
which typically extends through a side body of the injector. The
stepped bore defines a supply chamber and a valve bore. The valve
bore receives a valve stem of the associated control valve. The
valve bore may terminate in a chamfered valve seat. Similarly, the
valve stem may terminate in a head that seats against the valve
seat under the force generated by the solenoid. The head is
configured to mate closely with the valve seat. At least a portion
of the valve stem is subject to the high pressure generated in a
valve opening direction during an injection cycle. Accordingly, the
solenoid must generate sufficient force in the valve closing
direction to overcome such pressure. These forces are borne by the
valve seat through the head of the control valve.
While the design and operation of fuel injections have continued to
progress, there remains a constant need to improve fuel economy and
reduce emissions while at the same time reducing engine noise
induced from the operation of the fuel injector.
SUMMARY OF THE INVENTION
The invention results in improvements in the design and operation
of fuel injectors of the related art. More specifically, the
invention includes a method for controlling an electromagnetic fuel
injector assembly for an internal combustion engine. The fuel
injector assembly includes an injector body having a control valve
in fluid communication with a source of fuel for metering
predetermined quantities of fuel to a nozzle assembly. The control
valve is supported within a valve bore in the injector body and
includes a solenoid connected to a source of electrical current and
a valve member operatively connected to the solenoid and subject to
the pressures developed in the injector for moving the valve member
against a biasing force between open and closed positions. The
valve bore includes a relieved portion. The solenoid responds to
control signals developed by an electronic processor controlled by
software using an algorithm with input variables determined by
engine operating conditions. A regulated current for the solenoid
from a source of electrical current is developed at preselected
times during an injection event to slightly unseat the valve in
response to forces acting on the valve member in the valve opening
direction to regulate the injection pressure and the injection rate
of the fuel injector assembly. The valve member or the valve bore
may include a relieved portion, which results in a reduced surface
area contact between the valve head and the valve seat.
The method includes the step of providing a first level of
regulated current to the solenoid actuator to cause the valve to
partially seal the high pressure nozzle assembly passage from a
fluid pressure spill passage, thereby allowing the regulated
pressure in the nozzle assembly to rise to an initial injection
pressure. A reduced level of regulated current then reduces the
sealing force of the valve to create a reduced initial injection
pressure. An increased level of regulated current greater than the
first level then allows the regulated pressure to rise to a peak
value and create a peak injection rate controlled period near the
end of the injection event. That is followed by controlling the
current to effect a controlled decrease in injection pressure and
injection rate at the end of the injection event.
One advantage of the present invention is that the method controls
the injection rate and injection pressure of the electromagnetic
fuel injector assembly for calibrated injection times using
software to control the levels of current directed to the solenoid
during calibrated pressure regulation and to control the duration
of the regulation.
Another advantage of the present invention is that by controlling
the initial injection rate in diesel engines, the initial
combustion rates may be reduced to lower engine noise and reduce
NO.sub.x emissions.
Still another advantage of the present invention is that by
regulating the maximum injection pressure, the cam and plunger
associated with the injector assembly may be sized to provide high
injection pressures at low speed and load thereby improving fuel
economy and reducing soot formation while, at the same time,
preventing excessive structural loads at higher speeds and loads
through the pressure regulation function.
Still another advantage of the present invention is that the
depressurization rate of the fuel injector may be controlled. More
specifically, reducing the depressurization rate or spill rate
reduces the mechanically induced engine noise caused by the rapid
unloading of the drive system. This feature is applied by the
present invention by lowering the current to the solenoid at the
end of the injection event thereby slightly unseating the valve
member prior to fully terminating the current to the solenoid. By
regulating the current to the solenoid at the end of the injection
event, the acceleration forces acting on the valve member in the
valve opening direction may be reduced resulting in a reduced
depressurization rate.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages of the invention will be readily appreciated as
the same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
FIG. 1 is a partial cross-sectional side view of an electromagnetic
fuel injector;
FIG. 2a is a partial cross-sectional side view of a conventional
valve member of a solenoid-actuated control valve for an
electromagnetic fuel injector;
FIG. 2b is an enlarged, partial cross-sectional side view of the
valve member illustrated in FIG. 2a;
FIG. 2c is a partial cross-sectional side view of a valve member of
a solenoid-actuated control valve for the present invention
illustrating a relieved portion in the valve bore thereof;
FIG. 2d is an enlarged, partial cross-sectional side view of the
valve member of FIG. 2c;
FIG. 2e is a partial cross-sectional side view of a valve member of
a solenoid-actuated control valve of the present invention
illustrating the relieved portion on the head of the valve
member;
FIG. 2f is an enlarged, partial cross-sectional side view of the
valve member of FIG. 2d; and
FIG. 3 is a graphical representation of the movement of the control
valve as a function of solenoid current with reference to the
injection pressure over time.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is generally shown at 10 an
electromagnetic fuel injector assembly of the type commonly
employed in injectors with an internal combustion engine wherein
fuel is injected into a plurality of cylinders where it is
combusted to generate power to rotate a crankshaft. More
specifically, fuel injector assembly 10 shown in FIG. 1 has an
electromagnetically-actuated, pressure-balanced control valve
incorporated therein to control fuel discharge from the injector
nozzle portion of assembly 10 into a cylinder of the engine (not
shown) in a manner to be described. As illustrated in this figure,
the electromagnetic fuel injector assembly 10 includes an injector
body 12, which has a vertical main body portion 14 and a side body
portion 16. The main body portion 14 includes a stepped,
cylindrical bore 20 therethrough. The stepped, cylindrical bore 20
includes a pump cylinder 22, which slidably receives a pump plunger
24. In addition, the stepped, cylindrical bore 20 includes an upper
wall 26 of larger internal diameter to slidably receive a plunger
actuator follower 28. The plunger actuator follower 28 extends out
one end of the main body 14 whereby it and the pump plunger 24
connected thereto are adapted to be reciprocated by an engine
driven cam or rocker as known in the art. A stop pin (not shown)
extends through an upper portion of the main injector body portion
14 into an axial groove in the plunger actuator follower 28 to
limit upward travel of the follower under the bias of a plunger
return spring 34.
A nut, generally indicated at 36, is threaded to the lower end of
the main body portion 14 and forms an extension thereof. The nut 36
has an opening 38 at its lower end through which extends the lower
end of a combined injector valve body or nozzle assembly, generally
indicated at 40. The nozzle assembly 40 includes a spray tip 42.
The nozzle assembly 40 may include a number of elements, which are
well known in the art and which form no part of the present
invention. Accordingly, the inner workings of the nozzle assembly
40 will not be described in detail here.
The delivery of fuel from a source such as a fuel tank to the
nozzle assembly 40 is controlled by means of a solenoid-actuated,
pressure-balanced valve, generally indicated at 44 in the side body
portion 16. The side body portion 16 is provided with a stepped
vertical valve bore, generally indicated at 46, which defines a
supply chamber 48 and an intermediate or valve stem guide portion
50. The guide portion 50 of the valve bore 46 terminates in a valve
seat 52. The valve seat 52 is chamfered so as to define an angle
relative to the centerline of the valve bore 46. The valve 44 is
received within the stepped vertical valve bore 46 and includes a
valve member having valve stem 60 terminating in a head 54, which
seats against the valve seat 52. The stem 60 extends upward from
the head 54. A closure cap 56 is mounted to the underside of the
side body portion 16 and forms therewith a spill chamber 58.
The valve 44 is normally biased in a valve opening direction,
downward with reference to FIG. 1, by means of a coil spring 62,
which loosely encircles the valve stem 60. One end of the spring 62
abuts against a washer-like spring retainer 64 encircling the valve
stem 60. The other end of the spring 62 abuts against the lower
face of a spring retainer 66. Movement of the valve 44 in the valve
closing direction, upward with reference to FIG. 1, is effected by
means of a solenoid assembly, generally indicated at 68. The
solenoid assembly 68 includes an armature 70 having a stem 72
depending centrally from its head. The armature 70 is secured to
the valve 44.
As commonly known in the art, the solenoid assembly 68 may further
include a stator assembly having an inverted cup-shaped solenoid
case 74. A coil bobbin supporting a wound solenoid coil and a
segmented multi-piece pole piece are typically supported within the
solenoid case 74. The solenoid coil is connected through electrical
connectors 76 to a suitable source of electrical power via a fuel
injection electronic control circuit (not shown) under the control
of a software algorithm using input variables that are determined
by engine operating conditions. Thus, the solenoid coil can be
energized as a function of engine operating conditions, as will be
described in greater detail below.
A high pressure fuel passage, generally indicated at 78, provides
fluid communication between the control valve 44 and the fuel
nozzle assembly 40. As shown in FIG. 1, the fuel passage 78 is
formed by drilling a hole from one side of the side body portion 16
of the injector body 12 and between control valve 44 and the
stepped cylindrical bore 20. In this way, the fuel passage 78
defines a delivery portion 80 extending between the control valve
44 and the stepped cylindrical bore 20 and a portion 82 extending
between the valve stem guide portion 50 in the control valve 44 and
the side body portion 16. A plug 84 seals the open end of the
portion 82 of the high pressure fuel passage 78.
As illustrated in FIG. 1, the valve member, including the valve
stem 60 and at least a portion of the head 54, are subject to high
pressure via the delivery portion 80 of the fuel passage 78
developed by the injector. Thus, when energized, the solenoid
assembly 68 moves the valve member toward the closed position
against the biasing force of the spring 62 and the pressures acting
on the valve member via the fuel passage 78.
Referring now to FIGS. 2a and 2b, a conventional valve member
movably supported in the guide portion 50 of the valve bore 46 is
disclosed. The head 54 of the valve member is held against the
valve seat 52 and against forces acting on the valve in the valve
opening direction by the solenoid assembly 68. However, as shown in
FIGS. 2c and 2d, the guide stem portion 50 of the valve bore 46 may
include a relieved portion 86, which is subject to the pressures
developed in the injector to provide forces acting on the valve
member in the valve opening direction. Alternatively, as shown in
FIGS. 2e and 2f, the head 54 of the valve 44 may include a relieved
portion 90, which results in reduced surface area contact between
the head 54 and the valve seat 52. Either of the relieved portions
86 on the guide stem portion 50 of the valve bore 46 or the
relieved portion 90 on the head 54 of the valve member may be
employed to balance the control valve 44 in the following
manner.
During any given injection event, the solenoid assembly 68 may be
subject to reduced current from the source of electrical current at
preselected times to slightly unseat the valve member in response
to the forces acting on the valve member in the valve opening
direction and, in this way, to regulate the injection pressure and
injection rate of the fuel injector. More specifically, and
referring now to the graphs of FIG. 3, the movement of the control
valve 44 as a function of the solenoid current is illustrated with
reference to the injection pressure over time. As noted above,
initiation of current at 92 supplied to the solenoid moves the
control valve 44 in the valve closing direction as indicated at 94.
The pressure in the injector begins to rise as shown at 96.
Employing the method of the present invention, during the
initiation of the injection pressure, the current to the solenoid
may be reduced at 98 to slightly unseat the valve member
represented at 100 thereby controlling the rate of injection of the
fuel and fuel pressure as indicated at 101. The current to the
solenoid may then be increased again as indicated at 102 thus
moving the valve member to its closed position as indicated at
104.
Thereafter, when the pressure in the injector approaches the peak
injection pressure as indicated at 106, the level of current to the
solenoid may be reduced as indicated at 108 to slightly unseat the
valve member as indicated at 110 thereby regulating the maximum
pressure in the injector. At the end of the injection cycle, the
level of current to the solenoid may again be reduced as indicated
at 112 to slowly unseat the valve assembly shown at 114 thereby
controlling depressurization of the injector as indicated at 116.
More specifically, the rate of depressurization at 116 is slowed
when compared with the depressurization of conventional injectors
shown in dotted lines at 118. Finally, once the injection event is
completely over, the current to the solenoid is ended thereby
moving the valve member to its open position under the influence of
the spring 62 and any pressure existing in the fuel passage 78.
In this way, the injection rate and injection pressure in the
electromagnetic fuel injector assembly may be controlled. The
length of injection time and the level of current directed to the
solenoid during the regulation modes determines the level of
pressure regulation and the duration of the regulation. However, by
increasing current to the solenoid at any time, valve sealing can
be reestablished to resume traditional injection functions.
Additionally, by controlling the initial injection rate in diesel
engines, the initial combustion rates may be reduced to lower
engine noise or reduce NO.sub.x emissions. Furthermore, by
regulating the maximum injection pressure, the cam and plunger
associated with the injector assembly may be sized to provide high
injection pressures at low speed and load thereby improving fuel
economy and reducing soot formation while, at the same time,
preventing excessive structural loads at higher speeds and loads
through the pressure regulation function. Finally, the
depressurization rate of the fuel injector may also be accurately
controlled. More specifically, by reducing the depressurization
rate or spill rate, the mechanically-induced engine noise caused by
the rapid unloading of the drive system may be reduced. This
feature is achieved by the present invention through lowering the
current to the solenoid at the end of the injection event thereby
slightly unseating the valve member prior to fully terminating the
current to the solenoid. By regulating the current to the solenoid
at the end of the injection event, the accelerating forces acting
on the valve member in the valve opening direction may be reduced
resulting in reduced depressurization rates.
The invention has been described in an illustrative manner. It is
to be understood that the terminology which has been used is
intended to be in the nature of words of description rather than
limitation.
Many modifications and variations of the invention, as well as
equivalents thereof, are possible in light of the above teachings.
Therefore, within the scope of the appended claims, the invention
may be practiced other than as specifically described.
* * * * *